Synthesis, microstructure, and dielectric properties of novel dual-phase high-entropy (Ba0.2Ca0.2Sr0.2Na0.2Bi0.2)WO4 ceramics for LTCC applications

Novel dual-phase high-entropy (Ba 0.2 Sr 0.2 Ca 0.2 Na 0.2 Bi 0.2 )WO 4 ceramics were designed to reduce the sintering temperature and optimize the frequency temperature coefficients of scheelite-type AWO 4 ceramics. XRD and Rietveld refinement analyses revealed that the ceramic contained dual phases of BaWO 4 and Na 0.5 Bi 0.5 WO 4 . The phases had a tetragonal structure with the I4 1 /a space group, as verified by TEM. With increasing sintering temperature, the ɛ r exhibited a decreasing trend owing to the combined influence of ionic polarizability and density. In addition, the variation trend of the Q × f value was similar to that of the density, and its intrinsic influence was investigated by analyzing the FWHM of the Raman vibrational peak. The τ f was well optimized and exhibited a variation trend similar to those of the lattice distortion and microstrain. Finally, the (Ba 0.2 Sr 0.2 Ca 0.2 Na 0.2 Bi 0.2 )WO 4 sintered at 950 °C had the outstanding properties: ɛ r of 13.8, Q×f of 33,110 GHz and τ f of −34 ppm/°C at 9 GHz.